Sodium cooled reactors are known. An example of such a sodium cooled reactor is disclosed in Hunsbedt U.S. Patent Application Ser. No. 051.332 filed May 19, 1987 and entitled Control of Reactor Coolant Flow Path During Reactor Decay Heat Removal now U.S. Pat. No. 4,767,594. Simply stated, this reactor requires two separate liquid sodium loops for the extraction of heat from the atomic reaction occurring within the reactor.
The first sodium loop is radioactive, and maintained at approximately the atmospheric pressure. This radioactive primary loop is driven by submerged electromagnetic (EM) pumps. Liquid sodium is pumped upwardly and centrally through the reactor core, which core is placed concentrically to a large upstanding cylindrically reactor vessel. The heated primary sodium then transports the heat of the atomic reaction to kidney shaped intermediate heat exchangers. The primary sodium downflows through the kidney shaped intermediate heat exchangers on the outside of the reactor vessel. The cooled radioactive sodium then passes downwardly to the bottom of the reactor vessel, to the inlet of the electromagnetic pumps. These pumps then pump the cool radioactive sodium upwardly and through the core of the reactor for endless repetition of the heat transfer cycle.
The secondary sodium loop is not radioactive. This loop functions to extract heat from the sodium cooled reactor and to transport that heat to the steam generation system where steam may be generated.
The sodium in this second loop, also maintained at approximate atmospheric pressure, passes outside of the reactor to the steam generator. Heat of the sodium is liberated to feedwater to generate steam. Thereafter the cooled sodium passes to a typically mechanical pump. At the pump the now cooled sodium is returned to the reactor for endless repetition of the cycle.
It will be understood that sodium and the metallic vessels which contain sodium differentially expand. Thus, the secondary sodium loops are required to have an expansion vessel. These vessels are usually placed in the vicinity of the steam generator.
Further, the secondary loop on sodium cooled reactors have heretofore had three separate units. These units have included the steam generator, the pump and the expansion tank.
It has been proposed to place heat exchangers in side-by-side relation to nuclear reactors. See Bonsel et al. U.S. Pat. No. 3,425,907. This unit includes the primary and secondary sodium loops and the heat exchange therebetween. Unlike the present invention, it is not concerned with steam generation or surge volumes.
Kube U.S. Pat. No. 3,882,933 discloses a gas cooled reactor. The reactor includes helical windings.
A heat exchanger and sodium heated steam generator is disclosed in Robin et al. U.S. Pat. No. 4,307,685. In this reactor helical coils between inner and outer vessel are utilized. Here, however, the inner vessel is utilized as a flow distributor to facilitate heat exchange. A similar scheme is utilized by Jullien U.S. Pat. No. 4,515,109 the central vessel being constructed to resist sodium water transients.
Robbin U.S. Pat. No. 4,056,439 entitled Secondary Heat Transfer Circuits for Nuclear Reaction Plant issued Nov. 1, 1977 discloses a heat exchanger having first and second concentric vessels. One vessel is exterior. The remaining vessel is interior, open at the bottom and smaller and concentric of the larger vessel.
In the interstitial volume between the outer larger vessel and the smaller, concentric inner vessel, steam generation tubes are helically wound. These steam generation tubes begin at a tube sheet immersed in the liquid sodium at the bottom of the interstitial volume between the inner and outer vessel. These same tubes end in a tube sheet immersed in the liquid sodium at the top of the interstitial volume between the inner and outer vessel.
Pumping is suggested in two formats.
First, a pump is mounted at the top of the small vessel. This pump draws a suction on the liquid sodium the entire length of the small, concentric inner vessel.
Second, pumping by an impeller mounted at the end of a long rotating shaft is also disclosed. This long rotating shaft enables the impeller to be placed within the inner concentric vessel where the pump is more efficiently located.
Unfortunately, for both pumping schemes rotating bearings immersed in liquid sodium are required. These bearings require the introduction of high pressure sodium for lubrication. Further, such bearings upon stopping and starting are subjected to high degrees of wear.
The Robin U.S. Pat. No. '439 reference also exposes the tube sheets at the steam exit ends of the steam generating coils directly to the liquid sodium. Such exposure, due to the high thermal conductivity of the liquid sodium, can subject the tube sheets at the steam exit to thermal shock when thermal transients in the sodium loop do occur. Such thermal shock can lead to loss of fluid tight seal across the sodium water boundaries and cracking of the tube sheets themselves.
Finally, Robin requires a pump motor be added to the total height of the resultant steam generator. Vertical space is consumed for the motor and its required supplemental bearings, seals, flange plates and the like.